white growth on live rock

[untamed]

Are you sure that white stuff is alive in some way? It looks (to me) a lot like bare, dead rock. It's possible that the coraline covering has been killed off. What I'm trying to say is...that is what the rock would look like if it were completely barren of life. If that is the case, there's not much you need to do except wait for the tank to stabilize and the coraline will regrow.

If it is fuzzy, white then it could be a kind of mold that is common when you add new LR. If so, blow it off with a baster.